Since polyphenylene ether based resins are excellent in light weight, processability, electrical insulation, etc., they are widely used in the automobile field, appliance field or OA instrument field, etc. The polyphenylene ether based resins have a defect such that the rigidity thereof is low as compared with metals, and therefore, a technique of blending it with an inorganic filler for the purpose of enhancing its rigidity is generally employed. In the case where an inorganic filler is added to a polyphenylene ether based resin, though the rigidity or mechanical strength is enhanced, the impact resistance and surface smoothness are lowered. Since polyphenylene ether based resins are amorphous resins, a degree of deterioration in the surface smoothness and impact resistance is extremely large compared with crystalline resins such as nylon resins and polyester resins, and therefore, this is a serious problem.
There is disclosed a technique in which a polyphenylene ether resin is blended with an impact resistance improving agent such as a styrene-butadiene-styrene ternary block copolymer or a hydrogenated product thereof and a clay having specific particle size and surface area, thereby obtaining a material provided with strong toughness (see Patent Document 1). However, according to such a technique, it is impossible to sufficiently avoid deterioration in strong toughness and surface smoothness due to the clay.
There is disclosed a technique of improving a balance between rigidity and impact resistance in blending a thermoplastic resin with an inorganic filler by carrying out the blending so that 30% or more of the interface of the inorganic filler particle is brought into contact with an elastic polymer (see Patent Document 2). As a specific example of the method of bringing the elastic polymer into contact with the interface of the inorganic filler particle, there is described a method in which talc having been surface treated with γ-glycidoxypropyl trimethoxysilane or γ-(2-aminoethyl)aminopropyl trimethoxysilane and a maleic anhydride-modified ethylene-propylene copolymer or a silane-modified ethylene-ethyl acrylate copolymer are previously mixed in the form of solution or in a molten state, and the mixture is then melt kneaded together with a thermoplastic resin such as nylon 6 and polybutylene terephthalate. In this case, according to the simultaneous melt kneading of the inorganic filler, the elastic polymer and the thermoplastic resin, the desired effect is not obtained. In the description of Patent Document 2, though polyphenylene ether resins are mentioned as an example of the thermoplastic resin. However, as can be seen from the working examples thereof, the description thereof is directed to an improved technique for crystalline resins such as nylon 6 and polybutylene terephthalate, and does not provide a technique for enhancing the balance between rigidity, impact resistance and surface smoothness of amorphous resins which suffer from an extremely large degree of deterioration in surface smoothness and impact resistance due to an inorganic filler as compared with crystalline resins. In addition, it is not preferable to previously mix the inorganic filler and the elastic polymer in a solution state because it takes time and large expense to dissolve the elastic polymer using a solvent and then removing the solvent. Also, the method of previously melt kneading the inorganic filler and the elastic polymer is not preferable, because not only is the method expensive, but also the method results in the deterioration of the impact resistance due to thermal deterioration of the elastic polymer.
There is disclosed a technique of improving the balance between impact strength, mechanical strength, tackiness and appearance by a composition composed of a primary or secondary amino group-containing hydrogenated conjugated diene compound-aromatic vinyl compound block copolymer and at least one kind of a non-polar polymer, a polar polymer, and a filler (see Patent Document 3). In the description of Patent Document 3, polyphenylene ether resins are described as an example of the non-polar polymer, and it is disclosed that inorganic fillers such as kaolin as examples of the filler may be silane-treated materials. However, as can be seen from the working examples thereof, the description thereof is directed to an improved technique for crystalline resins such as polyethylene terephthalate, polypropylene, polyamides, and blends of polypropylene and polymethyl methacrylate. Also it does not provide any example in which an inorganic filler is blended. Thus, it does not demonstrate an improved technique for a resin composition mainly comprising a polyphenylene ether resin and an inorganic filler.    Patent Document 1: JP 57-502063 T    Patent Document 2: JP 8-53624 A    Patent Document 3: European Patent No. 1245585A2